This invention relates to the manufacture of composit products from sugarcane bagasse, sorghum stalks, corn stalks, sunflower stalks, flax stalks and other lignocellulosic materials, specifically of non-woody plants containing sugars, carbohydrates, or saccharides, which are water soluble and easily extracted.
More specifically, the invention relates to the manufacture of composite products from sugar containing lignocellulosic materials such as sugarcane bagasse, sorghum stalks, corn stalks, sunflower stalks, flax stalks and the like, without the addition of adhesive binders or bonding agents. This is accomplished by utilizing the free sugars, carbohydrates or saccharides as both bonding and bulking agents with the application of heat.
In the conventional manufacture of sugarcane bagasse panel products, synthetic thermosetting resin binders such as phenol-formaldehyde and urea-formaldehyde have been traditionally used, with the more expensive phenol-formaldehyde being employed for exterior grade products. Conventional resin binders account for a large portion of the total material cost of composite products. It is economically attractive to have composite products made without the use of expensive resin binders. Furthermore, a binderless manufacturing system simplifies the manufacturing process, and reduces production cost by eliminating the blending operation and equipment. Therefore, the desirability of using a binderless process in the manufacture of composite products will be readily appreciated from both economical and technological points of view.
In the conventional manufacturing process of bagasse panel products, the removal of pith and residual free sugars is essential to good quality panel products. The pith, as compared to true fibre, is a very short and thin-walled cell and contains a higher portion of sugars but contributes no strength to the final product. Because it is fluffy, the pith will absorb excessive resin binder particularly when liquid resin is used. Pith also acts like a sponge and soaks up water, swelling excessively if not removed from the bagasse composite panel products. Also, bagasse normally contains from 2 to 6 percent residual sugars, depending on the variety of cane, its maturity, method of havesting and finally, the efficiency of the sugar milling plant. The residual sugars in bagasse, if not removed or minimized before processing, may cause problems in board manufacturing and subsequently in service. Sugars may not be chemically compatible with the conventional resin binders used in bagasse board production and may interfere with bonding, resulting in poor strength. If the residual sugars are not chemically modified or consumed during hot pressing, they may start to ferment when the bagasse board is exposed to humid conditions, thus producing an unpleasant odor and culminating in chemical and biological degradation. This would essentially shorten the useful life of the bagasse board in service.
Consequently depithing and desugaring operations are necessary if satisfactory products are expected to be manufactured from sugarcane bagasse. These operations not only increase the manufacturing cost but also complicate the process.